1. Field of the Invention
The present invention relates generally to internal combustion engine controllers that drive loads using a high voltage obtained by boosting a battery voltage in an automobile, motorcycle, agricultural tractor, machine tool, marine engine, or other machines fueled with gasoline, a light oil, or the like. More particularly, the invention concerns an internal combustion engine controller suitable for driving an in-cylinder direct injection type of injector.
2. Description of the Related Art
Conventionally, in the automobiles, motorcycles, agricultural tractors, machine tools, marine engines, and other machines fueled with gasoline, light oil, or the like, injectors for injecting the fuel directly into cylinders are used to improve fuel efficiency and engine output. Such an injector is called the in-cylinder direct injection type of injector or simply called the direct injection (DI) type of injector. The engines employing the in-cylinder direct injection type of injector need to use a fuel that has been pressurized to a high pressure, so these engines require high energy for the valve-opening operation of the injector, compared with the gasoline engines of the currently prevailing scheme that create an air-fuel mixture and inject the mixture into a cylinder. In addition, the high energy must be supplied to the injector within a short time to improve controllability and generate higher engine speeds.
FIG. 9 shows an example of a conventional internal combustion engine controller designed to control the injector. The controller of the scheme shown in FIG. 9 has a voltage boost circuit 100 to boost a battery voltage 1 to a higher voltage and uses the thus-generated boost voltage 100A to enhance the signal level of the current supplied to the injector 3. Most of the conventional controllers for controlling the injector of an internal combustion engine employ this scheme.
The typical current signal waveform that the in-cylinder direct injection type of injector forms is the injector current signal waveform 3A shown at the bottom of FIG. 2. The injector uses a boost voltage 100A to raise the injector current signal 3A to a predetermined peak current deactivation level 460 within a short time during the initial phase of a peak current supply period 463. This peak current level is about 5 to 20 times as great as the injector current level achieved in the currently prevailing gasoline engine scheme for creating an air-fuel mixture and injecting the mixture into a cylinder.
After the foregoing peak current supply period 463, the source of energy supply to the injector 3 changes from the boost voltage 100A to the battery power supply first and then the hold current 1 controlled by a hold-1 deactivation current 461 of a level about ½ to ⅓ of the peak current level, and further changes to the hold current 2 controlled by a hold-2 deactivation current 462 of a level about ⅔ to ½ of that of the hold-1 deactivation current 461. The injector 3 uses the peak current and the hold current 1 to open the valve and inject the fuel into a cylinder.
It is necessary to cut off the injector supply current 3A by shortening a supply current fall period 466 thereof to close the valve of the injector more rapidly during the end of the injection. However, high energy is stored within the injector 3 because of the injector current 3A flowing therein, and to reduce the current level, it is necessary that the energy be made to disappear from the injector 3. Various schemes are adopted to achieve this within the short fall period 466 of the injector supply current 3A. In one scheme, the driving element of a driving circuit 200 for driving the injector current converts the energy into thermal energy using a Zener diode effect. In another scheme, a voltage boost capacitor 111 for storing the boost voltage 100A of the boost circuit 100 regenerates the injector current 3A through a current-regenerating diode 2.
The above scheme that converts the energy into thermal energy can be used to simplify the driving circuit 200 possible, but is not suitable for a driving circuit of a large current since the current supply energy of the injector 3 is converted into thermal energy. The scheme that utilizes the regeneration by the voltage boost capacitor, on the other hand, makes the occurrence of heat in the driving circuit 200 relatively suppressible, even when a large current is supplied to the injector 3. Therefore, the latter scheme is commonly used in the engines fueled with a light oil and employing the direct injection type of large-current injector (these engines may also be called “common-rail engines”), and in the gasoline-fueled engines employing the in-cylinder direct injection type of injector.
The boost voltage 100A is controlled according to the particular valve-opening characteristics of the injector 3 by a voltage boost control circuit 120 so as to stay within a previously set voltage range. However, if the injector current 3A is circulated into the voltage boost capacitor 111 of the boost circuit 100 through the current-regenerating diode 2, the boost voltage 100A is likely to overstep the previously set voltage range and enter an overboost state. If this actually happens, the valve-opening characteristics of the injector 3 will be adversely affected. In addition, if power supply short-circuiting or other trouble occurs in the injector, the boost voltage 100A is likely to exceed the withstand voltage of the driving element or voltage boost capacitor 111 of the boost circuit 100 and result in circuit damage. In order to avoid these risks, as described in JP-A-2002-303185, a charge overvoltage detection circuit is provided so that if a charging voltage becomes an overvoltage, the charging operation will be stopped. However, once an overboost state has actually occurred, this state cannot be compensated for, so the above conventional technique has caused the situation that the arrival of the next injector supply current at the peak current level thereof has adverse effects upon the valve-opening characteristics of the injector.
In addition, an example in which, as described in JP-A-2003-319699, a scheme intended to prevent the occurrence of voltage overboost with a regenerated current in an electric power-steering system using a boost voltage, by providing an n-channel type of MOSFET Q2 as a switching element in parallel to a diode D2 equivalent to a charging diode 110-1, and returning the regenerated current to a battery power supply, is introduced as an application of an apparatus other than an injector. The electric power-steering system is an apparatus that drives a motor, and in this apparatus, current regeneration continuously occurs during motor slowdown. Based on the recognition that current regenerative control is underway during this period, boost voltage control for returning the current to the battery power supply is continuously conducted and the boost voltage is not used for driving. In contrast to this, internal combustion engine controllers that drive an injector alternate between injector driving that uses a boost voltage, and current regeneration after supply of the injector current. Additionally, general internal combustion engines have two to eight cylinders or more cylinders, not one cylinder only, and engines of the direct injection scheme use one or more injectors for each cylinder.
For these reasons, in the internal combustion engine controllers of the direct injection scheme that each drive a plurality of injectors, decreases in boost voltage 100A due to driving of the injector current 3A that uses the boost voltage, and rises in the boost voltage due to the current regenerated by the injector current occur in alternate or complex patterns, not continuously. Under these changes in the boost voltage, it is important that the boost voltage be continuously controlled to stay within a previously set voltage range. If the foregoing current regeneration occurs during a voltage boost recovery period 406 that compensates for a decrease in the boost voltage, since the current regeneration can be used as the energy for voltage boost compensation, returning the regenerated current to the battery power supply will only turn out to be ineffective. Unlike electric power-steering systems, therefore, the internal combustion engine controllers for driving an injector(s) do not allow control in which whether the regenerated current is to be returned from the voltage boost circuit 100 to the battery power supply is determined, depending upon whether current regeneration occurs.
Non-Patent Reference 1: Kazuo Shimizu, “Design for Regulated Power Circuit—Continuation”, issued in 1974 by the CQ Publishing Co., Ltd.